1. Field of the Invention
The present invention relates to a laser-marking medium, more specifically to a laser-marking medium that which enables marks which are vivid, light resistant, scratch resistant, water resistant, chemical resistant and other properties to be made at high speed by laser light irradiation.
2. Description of the Related Art
As printing methods for printing objects-to-be-printed, such as labels, packaging materials, etc., the printing method, thermal transfer method, ink jet method, etc. have been conventionally used.
The printing method prints by transferring solution-type ink to objects-to-be-printed by impressions of various types. This printing needs bothering operations, such as changes of impressions, supply of ink, adjustment of viscosities, takes time to dry the transferred ink, and has limits to printing on objects-to-be-printed on high speed lines and printing of small lots.
The thermal printing method prints by transferring ink on ink ribbon to objects-to-be-printed through an ink ribbon by a thermal head printer. Different from the above-described printing method, the thermal printing method does not use liquid ink, and accordingly does not require bothersome operations, such as the ink supply, viscosity adjustment, etc. However, the ink ribbon must be periodically replaced, which puts a limit to printing objects-to-be-printed on high speed lines. Shapes of objects-to-be-marked are limited. The thermal printing method increases printing costs in comparison with the printing method.
The ink jet method prints by injecting liquid ink through micronized diameter-nozzles and staying the ink on objects-to-be-printed. The ink jet method can print at high speed and make distinct prints, and accordingly can print objects-to-be-printed on high speed lines and can print small lots. However, on, e.g., high speed lines of filling and packaging food it is disadvantageous in terms of sanitariness that the ink jet method prints information, such as production dates, edible limits, lot numbers, production factories, etc., on objects-to-be-printed, such as labels, packaging materials, etc. Furthermore, the ink jet method is disadvantageous in maintenance, as of ink replacement, etc. which is attributable to its mechanism. The use of solvent-based ink for quick drying printed ink tends to coagulate the nozzles with a resulting in defective prints. On the other hand, the use of water-soluble ink, which does not easily coagulate, lowers the water resistance of prints.
Furthermore, in a case that objects-to-be-printed are labels for bottles for beverages, severe requirements are made of the objects-to-be-printed themselves in addition to the above-described disadvantages of the respective printing methods. That is, generally bottle loading lines for beverages are sped, and many of the bottles are hot-loaded, and the loaded, sealed and labelled bottles are carried on conveyors. During this process, the bottles collide with one another; often bottle coating liquids for hinding bottle scuffing are applied to the surfaces of the bottles, and furthermore the bottles are often immersed for cooling. Thus, the labels adhered to the bottles are placed in very severe environments. It is required that the labels can be resistant to such environments.
The labels used on the above-described beverage bottles includes, e.g.,
1) a label having indications, such as a production date, etc. is printed in advance together with pictures and patterns at a peripheral part thereof, and notches are made in the location for indication when a beverage is loaded;
2) a label having an ink that is colored by irradiating laser beams applied in advance to a label marking region; and
3) a label having in a label marking-region a color ink layer that is able to absorb energy of an applied laser beam at the irradiated parts thereof, and heat and removably break there, laser light being applied to the label marking region to remove the color ink layer in the shapes of letters, marks, etc., whereby a contrast of colors between the removed part and remaining part forms marks.
However, the above-described label 1) has disadvantages that when notches are cut to make indications, breakages are generated, and the label adhered to a bottle tends to easily start breaking, and other disadvantages.
The above-described label 2) has disadvantages that although high-speed marking is possible on the label 2), the colored ink layer has insufficient light resistance and chemical resistance, etc. and has a risk that when exposed to ultraviolet rays, the label 2) may be discolored. To prevent such an occurrence, in a case that an overprint layer is applied to the laser coloring ink layer, when the overprint layer is broken by excessive laser beam irradiation, marks are faded by application of a bottle coating liquid, etc. after the label is adhered. Disadvantageously, this treatment makes it difficult to adjust conditions of irradiating laser beams.
The above-described label 3) can be marked at high speed, but the marks lack visibility, and the colored ink layer at marking parts is completely removed. Accordingly, even if an overprint layer, for example, is formed on the color ink layer, the support element at the marking parts is exposed, and disadvantageously the marking parts have reduced scratch resistance and water resistance.
In view of the above-described circumstances, the present invention was made. An object of the present invention is to provide a laser-marking medium that can be distinctly marked by irradiating laser beams at high speed, and has good light resistance, scratch resistance, water resistance, chemical resistance, etc.
To achieve the above-described object, the laser-marking medium according to the present invention comprises laser-marking medium comprising a support element; a base layer formed on the support element and being capable of absorbing a laser beam; and a masking layer formed on the base layer and having a lightness distinctly different from that of the base layer.
In the laser-marking medium according to the present invention, the masking layer contains metal powder by 3-10 weight %.
In the laser-marking medium according to the present invention, the metal powder is aluminium, and the aluminium powder is of non-leafing type.
In the laser-marking medium according to the present invention, the white pigment is titanium oxide.
In the laser-marking medium according to the present invention, the base layer contains carbon black.
The laser-marking medium according to the present invention further comprises an overprint layer formed on the masking layer.
In the above-described invention, a laser beam applied to the laser-marking medium is absorbed by the base layer having a laser light beam-absorbing power, and then the base layer heats and breaks to remove the masking layer in the laser beam applied region, whereby a lightness difference is generated between the laser beam non-applied region of the masking layer containing metal powder and a white pigment, and the laser applied region where the masking layer is removed to make marks in the laser applied region distinctly visible.